This invention concerns piezoelectric ceramic resonant transducers in which a vibratory diaphragm member is edge mounted and carries a flat ceramic disk on at least one of its faces for sensing or driving flexure of the diaphragm.
Flexure of such a diaphragm assembly perpendicular to its plane is associated with radial stretching or compression of the ceramic. Those stresses are accompanied by electrical potentials of opposite polarity at the respective disk surfaces, corresponding to the piezoelectric properties of the material. Electrodes in contact with the opposite faces of the disk convey the electrical signal between the transducer and an external circuit of any desired type.
The invention is concerned more particularly with such transducers in which the diaphragm and its carried ceramic disk are free to flex in fundamental mode at their natural or resonant frequency of vibration. Under that condition the transducer is a highly sensitive detector of vibrations at that same frequency and can drive such vibrations with good efficiency in response to an input periodic electrical signal.
In order to insure optimum sensitivity of selective response at a sharply defined target frequency, whether for detection or generation of vibrations, it is important that the resonant frequency of vibration of the transducer match that target frequency as closely as possible.
The utility of such selectively responsive transducers has been limited in the past by difficulty in producing economical transducers having a well-defined resonant frequency that is satisfactorily uniform from one unit to another. Under conditions of mass production, especially when the production cost must be held to a minimum, individual transducers tend to differ in resonant frequency over a range that is excessive for many applications.
An effective solution for certain aspects of that difficulty is described and claimed in the copending patent application Ser. No. 927,546, which was filed under the title "Piezoelectric Ceramic Resonant Transducers with Stable Frequency" by Joe F. Guess, one of the present joint applicants, and which is assigned to the same assignee as the present application.